Final answer:
Plaque is a soft mass of bacterial deposits that covers the tooth surface. If not removed, it can harden and turn into tartar or dental calculus.
Step-by-step explanation:
The soft mass of bacterial deposits that covers the tooth surface is called plaque. Plaque is a sticky film that forms on the teeth when bacteria in the mouth interact with sugars and starches from food. If not removed through proper oral hygiene, plaque can harden and turn into tartar, also known as dental calculus.